This invention is directed to new nonlinear optical materials which may be used in optical devices, such as optical bistable devices which make use of nonlinear optical effects, and to methods for manufacturing these new materials.
Many nonlinear optical materials are known in the prior art. One class of such materials consists of semiconductor-doped glasses. For example, an optical cut-off filter fabricated from borosilicate crown glass doped with CdS.sub.x Se.sub.l-x has been shown to exhibit nonlinear optical properties. This filter was described in an article in The Journal Of The Optical Society Of America, Vol. 73, p. 647, published in 1983. The cut-off filter was manufactured by melting both CdS.sub.x Se.sub.l-x and a borosilicate glass material in a platinum crucible at a temperature of 1600.degree. C.
Another known nonlinear optical material consists of a glass thin film doped with CdS microcrystallites. This material was disclosed in The Journal of Applied Physics Vol. 63, p. 957, published in 1988. This thin film nonlinear material is deposited in a high-frequency magnetron sputtering apparatus, wherein a disc of 7059 glass (manufactured by Corning Glass Co.) and CdS powder are used as a composite sputtering target. During the sputter deposition process, about 2 to 4% by weight of CdS is diffused into the 7059 glass. However, the prior art manufacture of nonlinear materials in which optical glasses are doped with semiconductor materials has a number of major drawbacks.
For example, in the melting method used to fabricate the prior art cut-off filter material CdS.sub.x Se.sub.l-x and borosilicate glass material are melted together in a platinum crucible heated to a temperature of more than 1600.degree. C. At that high temperature, undesirable chemical reactions can occur. For example, the surface of the microcrystallites which form from the CdS.sub.x Se.sub.l-x semiconductor material may be oxidized upon reaction with residual gases in the reaction chamber or with the oxygen in the borosilicate glass. These deleterious reactions make control of the semiconductor composition highly difficult. Furthermore, with the melting method, it is also difficult to uniformly dope the borosilicate glass with the CdS.sub.x Se.sub.l-x semiconductor by more than 2 to 4 weight %.
If a sputtering method is used to manufacture an oxide-based glass thin film doped with semiconductor microcrystallites, as in the second example of prior art, the surface of the semiconductor will tend to oxidize during the sputtering process by reaction with the oxide glass. Moreover, the sputtering process is disadvantageous when a thick SiO.sub.2 glass film having a low sputtering rate has to be manufactured.